Current methods for quantitating blood flow in the myocardium are limited by inadequate attenuation correction, by partial volume corrections and by deadtime problems. Attenuation effects: During this year we have completed analysis of all the attenuation correction data. The results have been written up as a paper and submitted to the Journal of Nuclear Medicine as a full paper. It is currently in review. Partial Volume effects: This work involves using gated MRI imaging to predict the partial volume effects which occur during PET or SPECT imaging. We have collected gated spin echo MRI data, and corresponding PET data from 6 normal volunteers to date, and have discovered that the partial volume effect frequently causes an erroneous apparent drop in measured activity at the apex of the heart. In addition, the partial volume effect may alter the observed activity concentrations in the free wall relative to the apex. This would have important ramifications on the interpretation given to recently published FDG results in normals. We have presented this data orally and in abstract form at the 1991 Society of Nuclear Medicine meeting. The data will be submitted as a full article as soon as several additional subjects have been studied. Deadtime effects: This work has been described in last years progress report. Most of the data has now been accumulated, and a manuscript is in preparation.